I have the iPhone 6, running iOS 9.1, I had lots of videos (many were multiple minutes long) that took up too much space, I started with (according to my settings app) about 400 megabytes free, after posting the videos to youtube and deleting the videos from my phone, it says I still have about 400 megabytes free. Whats the deal? I've synced my phone to my computer and the iTunes program says I have 1.6 gigs free. Is my phone just displaying incorrectly?
iOS is keeping you safe by saving all deleted videos and photos in a special album called
Recently Deleted. The media files in there gets deleted after 30 days.
In order to free up the "imaginary space" that you think you got after deleting, empty out this album and you should see an increase of free space.